Made ElementRareData store ComputedStyle on LayoutObject if possible.

third_party/WebKit/Source/core/dom/ElementRareData.h

Index: third_party/WebKit/Source/core/dom/ElementRareData.h
diff --git a/third_party/WebKit/Source/core/dom/ElementRareData.h b/third_party/WebKit/Source/core/dom/ElementRareData.h
index fe196fb89ed539bba4cafc5fc5375e87f58407c6..957344a9724c4b7b2933a24f5389573374bc4d7f 100644
--- a/third_party/WebKit/Source/core/dom/ElementRareData.h
+++ b/third_party/WebKit/Source/core/dom/ElementRareData.h
@@ -91,8 +91,19 @@ public:
     NamedNodeMap* attributeMap() const { return m_attributeMap.get(); }
     void setAttributeMap(NamedNodeMap* attributeMap) { m_attributeMap = attributeMap; }
 
-    ComputedStyle* computedStyle() const { return m_computedStyle.get(); }
-    void setComputedStyle(PassRefPtr<ComputedStyle> computedStyle) { m_computedStyle = computedStyle; }
+    ComputedStyle* computedStyle() const
+    {

[Timothy Loh, 2016/09/07 04:56:07]

Maybe DCHECK(!(layoutObject() && m_computedStyle)) here

[Bugs Nash, 2016/09/13 21:46:55]

Done.

+        if (layoutObject())
+            return layoutObject()->mutableStyle();
+        return m_computedStyle.get();
+    }
+    void setComputedStyle(PassRefPtr<ComputedStyle> computedStyle)
+    {
+        if (layoutObject())
+            layoutObject()->setStyleInternal(computedStyle);
+        else
+            m_computedStyle = computedStyle;
+    }
     void clearComputedStyle() { m_computedStyle = nullptr; }

[Timothy Loh, 2016/09/07 04:56:07]

OK for now but at some point we should work out if we actually need this because
it's a bit weird. Please add a comment because otherwise it looks like it's just
doing the wrong thing.

[Bugs Nash, 2016/09/13 21:46:55]

As per offline conversation the usage of this method only works when there is no
LayoutObject. I did a dry run with all 3 call sites only calling this method if
there is no LayoutObject and it passed. I the ntried removing the check for a
LayoutObject in each of the 3 call sites 1 at at time and the bots failed for
all 3 (see https://codereview.chromium.org/2318973003). Therefore I think the
best solution is to keep the functionality in this patch and change the name of
this method to clearComputedStyleIfNoLayoutObject to make it clear that this
will not clear the ComputedStyle on the LayoutObject. I've also added a DCHECK
that there isn't simultaneously a LayoutObject and a separate ComputedStyle as
this may lead to unexpected behavior.

 
     ClassList* classList() const { return m_classList.get(); }